CHEMICAL ANALYSIS 15 



at rest, before any further manipulations are tried. There- 

 after more of the substance is added, and the same tech- 

 nique carefully observed. 



To obtain the weight of a substance or dish, or both, these 

 are placed in the left-hand pan, and a trial weight is put 

 on the right pan. If this is too much, the next lower 

 weight is tried, and so on, being careful to observe the 

 technique outlined above. The weight is read from the 

 vacant spaces in the case, and checked on removing the 

 weights. Always use a watch-glass in weighing a salt or 

 substance not contained in a vessel of some kind. 



Atomic Weights. The following table gives for some 

 of the elements the older atomic weight, and that more 

 recently assigned. 



OLDER 

 ATOMIC WEIGHT. NEWER. 



Aluminium . . . . 27 . . 26-9 



Arsenic . . . . . . 75 . . 74-4 



Barium . . . . . . 137 . . 136-4 



Boron . . . . . . n . . 10-9 



Bromine . . . . . . 80 . . 79-4 



Calcium . . . . . . 40 . . 39-7 



Carbon . . . . . . 12 . . 11-9 



Chlorine 35-5 . . 35-1 



Copper . . . . . . 63 . . 63-1 



Hydrogen . . . . . . i 



Iodine . . . . . . 127 . . 126-0 



Iron 56 .. 55-5 



Lead . . . . . . 207 . . 206-4 



Magnesium . . . . . . 24 . . 24-18 



Manganese 55 .. 54-52 



Mercury . . . . . . 200 . . 198-5 



Nitrogen . . . . . . * 14 . . 13-9 



Oxygen . . . . 16 . . 15-9 



Phosphorus . . . . 31 . . 30-8 



Potassium . . . . . . 39 . . 38-8 



Silver . . . . . . 108 . . 107-1 



Sodium . . . . . . 23 . . 22-9 



Sulphur . . . . . . 32 . . 31-8 



Tin . . . . . . 118 . . nS-i 



Zinc . . . . . . 65 . . 64-9 



